Sewer gas is a rich source of hydrogen sulfide. With a passive iron filter, the sulfur bonds with iron freeing up the hydrogen. I did this in a small jar successfully. Iron sulfate is a fertilizer for blueberries, azaleas, and other acid-loving plants. You'd be reclaiming waste water instead of wasting it and this demands no added energy like splitting water molecules to get hydrogen does.
Wastewater treatment has been strictly a province of city government and because this is not a proprietary process, no business would be interested in using it commercially. Alternative substances besides iron would be copper to generate cupric sulfate (used commercially to kill roots in sewer systems and for copper plating, etc), and silver, which would just tarnish.
Silver would be re-usable.